Intraocular lenses (IOLs) have been widely used after patients undergo surgical cataract removal. In 2003, there were approximately 15 million IOLs sold worldwide, including 2.5 million in the US. The standard IOL today is made from biocompatible foldable polymers containing a UV absorber. Such an IOL can filter out UV A (200-315 nm wavelength) and UV B (315-380 nm wavelength) effectively to provide sufficient protection for the patient as far as UV light damage is concerned.
In recent years, there have been some concerns about potential blue light damage to the retina. For this reason, Alcon Laboratories, Inc. introduced ACRYSOF® Natural into the U.S. market in 2003. ACRYSOF® Natural is a foldable IOL made from a hydrophobic acrylic copolymer containing both a UV absorber and a blue light absorber. It not only absorbs UV light but also blue light. The theoretical basis for ACRYSOF® Natural is that blue light (400 nm to 470 nm) has been demonstrated to cause damage to retinal pigment epithelial cells in vitro, as well as in some animal studies. Since age-related macular degeneration is caused by the degeneration of the retinal pigment epithelial cells, blocking blue light from reaching the retina, such as by blue light absorbing IOLs, might reduce the risk for or progression of age-related macular degeneration. Nevertheless, the clinical implications of these theoretical analyses have not yet been determined.
The blue light-absorbing IOL has a yellow tint due to its absorption of blue light. In addition to the potential protective effect for the retina, the absorption of the short wavelength visible light (blue light) can enhance contrast when viewing bright objects against a blue-based background, such as the sky (see Janet R. Sparrow, et al, “Blue light-absorbing intraocular lens and retinal pigment epithelium protection in vitro”, J. Cataract Refract. Surg. 2004, 30:873-878). On the other hand, the yellow tint can compromise a patient's color perception, especially in a weak light environment, such as driving at night. Proponents suggest that the yellow tinted color provides senior patients, whose natural crystalline lens has become increasingly yellow due to aging, with natural color perception after their cataract lens is removed and replaced with the IOL. Critics argue that while it could be true that blue light absorbing IOLs may provide a patient with a natural view in a strong light environment, the decrease in color perception may compromise a patient's capability to drive at night and under other low light conditions. Accordingly, an ideal IOL would have a yellow color and absorb blue light in a strong light environment, such as an outdoor environment under a sunny sky, while under weak light conditions, such as indoors, the IOL would become colorless so that the patient could return to normal color perception. The goal of the present invention is precisely to provide such an ideal IOL for patients.
Photochromic spectacles have been widely used in the last decade. A photochromic spectacle darkens when exposed to UV light in an outdoor environment. When in an environment where there is no UV light, photochromic spectacles change back into a colorless state. Photochromic contact lenses have also been reported in the literature. U.S. Pat. No. 6,224,945, Calderara, issued May 1, 2001, discloses a process for manufacturing a crosslinked transparent hydrophilic polymer with photochromic dyes by impregnating the polymer material with a photochromic agent in an organic solvent and then rinsing the polymer with an aqueous solution. Calderara applied his invention to contact lenses. Those who are skilled in the art will understand that hydrophobic polymers, such as those used in IOLs, would typically not be appropriate for use in Calderara's method.
To our best knowledge, there has been no report of photochromic IOLs, particularly photochromic IOLs with blue light absorption in their activated state. There could be a number of good reasons why photochromic IOLs have not been explored. First, IOLs in the marketplace generally provide sufficient UV protection for both UV A and UV B, while the photochromic dye usually is used to lower the light transmittance of UV light and/or selected visible light range; the benefit for using a photochromic agent in an IOL is, therefore, not obvious. Second, there is a possibility that a photochromic agent may not change color inside the eye because there may not be sufficient UV light rays entering the eye through the cornea to activate the dye. The cornea is the first layer of protection to prevent hazardous UV light rays from entering the eyes and damaging the natural lens and retina. In spite of this uncertainty, the present invention has defined a suitable photochromic IOL wherein the photochromic agents are so sensitive that even inside the eye, they can be activated by the UV light rays entering through the cornea.